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Nervous System

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Scope

Humans have 1012 neurons You only have 109 DNA bases Typical cells are 10 microns in diameter Some of your neurons are 3 feet long The longest neurons in Giraffe 3 meters Complex program directs connections You photoreceptors can detect down to 1 photon -70 mV across 3nm is equivalent to 200,000V

across 1cm

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Animation

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1s1g

domains of Kv4 K(+) channels regulate binding to and modulation by KChIP1

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Myelin Sheath

Wraps around Multiple Sclerosis is an autoimmune attack on

myelin sheaths resulting in 100 times slower signal propagation along the axon

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Most neurons have a single axon – a long (up to 1m) process designed to convey info away from the cell body.

Transmit APs from the soma toward the end of the axon where they cause NT release.

Often branch sparsely, forming collaterals.

Each collateral may split into telodendria which end in a synaptic knob, which contains synaptic vesicles – membranous bags of NTs.

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Synaptic Transmission

An AP reaches the axon terminal of the presynaptic cell and causes V-gated Ca2+ channels to open.

Ca2+ rushes in, binds to regulatory proteins & initiates NT exocytosis.

NTs diffuse across the synaptic cleft and then bind to receptors on the postsynaptic membrane and initiate some sort of response on the postsynaptic cell.

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Figure 48.12 A chemical synapse

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SpinalCord

BrainSensoryNeuron

MotorNeuron

Motor Neurons

OUTPUT From the brain and spinal cord To the muscles and glands.

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Some Drugs work on receptors

Some drugs are shaped like neurotransmitters

Antagonists : fit the receptor but poorly and block the NT e.g. beta blockers

Agonists : fit receptor well and act like the NT e.g. nicotine.

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How did they figure this out?

Patch Clamping Put a really small pipette over a ion channel Suck up one ion channel so that the membrane

blocks the glass tube Measure the current flow as you vary voltage

across the ion channel Insert chemicals to see how they impact the

channel

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Muscle Interaction

Calcium channels activated by action potential in nerve

Cascade through muscle caused by interaction with one muscle

cellhttp://thevirtualheart.org/

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Sushi

Blowfish have a toxin that irreversibly binds and inhibits the voltage gated sodium channels

Paralyzes person who consumes it because you cant accomplish action potential

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Poison Darts

Tip with Curare Reversibly binds to acetylcholine receptor and

blocks connection between nerves and muscles

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Sarin

Inhibits acetylcholinesterase You cant relax your muscles